A. Field of Invention
The present invention relates generally to touch-screen displays, and more specifically to a high-resolution touch screen display with multi-touch capability either using electrical time domain reflection or optical time domain reflection profile.
B. Description of the Related Art
There are about a dozen technologies available in the field of touch screen sensor that applies onto display unit such as LCD (Liquid Crystal Display), CRT, and Plasma display and so on. ATM machine display unit and MP3 display in a consumer product are well known daily encountered examples of the field. Recently as a new technology advance in this field, ‘Multi-Touch’ capability has been added onto this conventional touch screen technology, which has created a new generation of this field in a way it shifts the paradigm of man machine interactive device as simple menu-driven single touch display interface to more versatile gesture interactive tool.
Among many other possible technologies, FTIR (frustrated total internal reflection) based multi-touch technology shown in U.S. Patent Application Publication US2008/0029691 A1 assigned to Jefferson Y. Han is noteworthy of its image sensing technology for multi-touch sensing. When fingers or any objects touch the overlay optical sensor surface which normally confines (infrared or invisible) the flooding light by TIR (total internal reflection) condition, the light start to emanate through the area of the frustrated TIR created by a touch (or multiple touches) event and at the same time the locations of light openings can be captured by external image array sensor or possibly embedded image sensors in LCD substrate as shown in FIG. 1. The captured locations of the touched areas are then to be signal-processed in a sequential time order to interpret the gesture for the finger motion through computer software. This invention, however, unless LCD panel manufacturer invest on embedded sensor array in TFT(Thin Film Transistor)—LCD array process, create extra volume to place the external camera at least in its focal distance to capture the image properly so that it makes the whole unit bulky which is not desirable for their thinner and wall-mountable purpose.
The projected-capacitive touch (PCT) technology is another popular and well known technology that has multi-touch capability. (FIG. 3) But because PCT uses ITO (indium tin oxide) metal layer on glass or in general any transparent material such as acrylic board, the brightness of overall display is diminished due to its opaqueness. Moreover, in order to keep a reasonable SNR (Signal-to-noise ratio) for touch sensitivity, increasing the size of screen will result in increasing the thickness of ITO layer, which makes the sensor panel even more opaque. This is especially critical for multi-ITO layers. This becomes why the technology is limited to the small handheld type of application. So it has been a challenge for PCT to be applied successfully into large flat panel display monitor such as Flat-Panel (FP) TV. The present invention is reducing or even removing such layer the number of ITO layers by applying Time domain reflectometer (TDR) processing.
SAW (Surface Acoustic Wave) technology can be another multi-touch touch screen method that are currently available and can be implemented to keep an optical transparency with reasonable size of display. SAW is using ultrasonic transducers with some sophisticated hardware or software implementation to keep the sensor linearity meaningful. Shadowing issue that makes the recognition of the second touch in the shadow region of the first difficult is another hurdle for multi-touch capability. Another technology that has shadowing effect is ‘infrared touch’ technology Infrared touch uses the infrared light source array at one side of display panel and the detector array at the opposite side of it as shown in FIG. 2. The infrared touch method is straight forward in a sense that it locates the touched area by looking at the shadow area of the opposite side of photo detector array but with the drawback of the shadowing effect. In other words, it has difficulty to tell the second touch behind the shadow.